The present invention relates to vacuum generator devices.
One of the common uses of vacuum generator devices is to generate a vacuum in an enclosure for processing semiconductors.
During such processing, material is deposited on or etching is performed in a semiconductor wafer. The efficiency of deposition is relatively low, and as a result the vacuum generator device sucks in a large fraction of the materials that are to be deposited on the semiconductor wafer. The vacuum generator device also sucks in the materials which are extracted from the semiconductor wafer during etching operations.
Vacuum generator devices comprise at least a primary pump which delivers pumped gas to atmospheric pressure or to a pressure that is relatively high. In such a primary pump, the pumped gases tend to condense and solidify in the form of deposits when their temperature is too low, or when temperature variations are too large. Those deposits interfere with the operation of the pump and the quality of the vacuum generated, and can give rise to pollution by being scattered back into the enclosure for processing semiconductors.
It is desired to limit the deposition of solids that results from condensation or solidification of gases by regulating the temperature of the pump body in a manner that is as stable as possible.
In known systems, the pump body is temperature regulated by a system for controlling the temperature of the vacuum pump and comprising at least one heat exchange circuit in which a heat-conveying liquid circulates, at least a first portion of the circuit being in thermal communication with the vacuum pump and a second portion of the circuit being in connection with a source of heat. Means are provided for causing the heat-conveying liquid to circulate in the heat exchange circuit.
In a first possibility, e.g. as described in document JP 11 280681, control means enable the flow rate of the heat-conveying liquid in the heat exchange circuit to be varied, thereby modulating the heat exchange capacity of the heat exchange circuit as a function of a control signal so as to match it to the heat exchange requirement for keeping the temperature of the pump in a suitable temperature range.
The amount of heat that needs to be exchanged to regulate the temperature of the pump leads to the flow rate of the heat-conveying liquid being varied very greatly. Thus, the speed of the heat-conveying liquid is variable, being low during certain operating stages, and its temperature is also variable and is high during certain operating stages.
In another possibility, control means serve to vary the power of the heat source, e.g. by adjusting the electrical current used for heating, as described in document JP 01 008388, or by adjusting the speed of a cooling fan, as described in document JP 07 174099. In all cases, the temperature of the heat-conveying liquid is highly variable as a function of the heat power to be conveyed.
A problem encountered in those known systems for controlling temperature is the deposition of scale in the pipework and in the parts to be cooled when ordinary public water supply water is used as the heat-conveying liquid. The lime naturally present in suspension in the water solidifies and forms deposits of scale in the pipework and in the parts to be cooled, initially spoiling heat exchange quality, and capable in the end of blocking said pipework or parts.
The problem proposed by the present invention is that of designing a novel structure for a temperature control system in vacuum generator devices to make it possible to ensure effective temperature regulation while avoiding the above-mentioned deposition of scale.
The idea on which the present invention is based consists in causing a heat-conveying liquid to flow in the heat exchange circuit continuously at a relatively high speed and at a relatively low temperature, regardless of the operating stages of the vacuum generator device, while providing means other than speed variation for regulating the temperature of the pumps.
The proposed principle is based on providing adjustable thermal conductance between the heat-conveying liquid and the vacuum pump. This makes it possible to keep the heat-conveying liquid circulating continuously at maximum flow rate and at low temperature, the flow rate being not less than the flow rate required for guaranteeing sufficient heat exchange under the extreme operating conditions of the vacuum pump.
To achieve these objects, and others, a vacuum generator device of the invention comprises at least a vacuum pump and a system for controlling the temperature of the vacuum pump, the temperature control system having at least one heat exchange circuit in which a heat-conveying liquid circulates and including at least one first circuit portion which is in thermal communication with the pump body of the vacuum pump, including circulation means for causing the heat-conveying liquid to circulate in the heat exchange circuit, and having control means for controlling the heat exchange capacity of the heat exchange circuit as a function of a control signal;
according to the invention:
heat conduction means having thermal conductance that is adjustable by the control means provide thermal communication between the pump body and the first circuit portion;
the control means are adapted to vary the thermal conductance of the heat conduction means so as to maintain the temperature of the pump body in the vicinity of a predetermined reference temperature;
the circulation means, for causing the heat-conveying liquid to circulate, are adapted to cause the heat-conveying liquid to circulate permanently in the heat exchange circuit at a flow rate that is not less than the flow rate required for providing sufficient heat exchange under extreme operating conditions of the vacuum pump.
In a first application, the heat exchange circuit is adapted to heat the vacuum pump. In which case, the device is used in those zones of the vacuum generator device where it is necessary to heat the vacuum line in order to avoid solids being deposited.
In a second application, the heat exchange circuit is adapted to cool the vacuum pump. The device is then used in those zones of the vacuum generator device in which pumping gives rise to excessive heating.
A combination of both applications can be provided, making it possible either to heat or to cool a given same zone of the vacuum generator device.
In an advantageous embodiment, the heat conduction means having adjustable thermal conductance comprise:
at least one adjustment chamber interposed between the first circuit portion and the pump body;
a source of thermal communication liquid, connected to the adjustment chamber, and adapted to feed the adjustment chamber with an adjustable quantity of a thermal communication liquid so as to adjust the heat exchange area occupied by the thermal communication liquid between the first circuit portion and the pump body.
In this case, the source of thermal communication liquid comprises a pipe for passing the thermal communication liquid, a supply of thermal communication liquid, and liquid adjustment means to cause the thermal communication liquid to pass between the adjustment chamber and the supply of thermal communication liquid.
The liquid adjustment means may comprise a piston disposed in the supply of thermal communication liquid and driven by an actuator controlled by a control member as a function of a temperature order signal and of pump temperature measurement signals coming from temperature sensors associated with the pump body.
In a practical embodiment, the adjustment chamber can be a cavity formed in the pump body with a heat exchange pipe passing therethrough, said pipe forming said first circuit portion, the cavity being closed by closure means making it leaktight relative to the atmosphere, the heat exchange pipe having at least one portion rising between two distinct extreme levels defining the extreme depth to which the thermal communication liquid can be adjusted.
Preferably, in order to make implementation easier, the adjustment chamber has two opposite ends and has the heat exchange pipe passing therethrough between a bottom orifice and a top orifice.
The adjustment chamber may be closed at its end(s) by one or more leaktight plugs, or by crimping around the heat exchange pipe.